1. Field of the Invention
The present invention relates to a color wheel suitable for use as a filter element of a time-share light dispersing device, and more specifically to a color wheel of segment type.
2. Description of the Related Art
Color composition in a projection-type image display apparatus has conventionally been accomplished commonly by a method, such as: a single-panel method, in which one light valve element adapted to control light amount per pixel thereby creating an image is used to disperse each pixel into R (red), G (green), and B (blue) lights; and a three-panel method, in which three light valve elements dedicated to R, G and B lights, respectively, are used to produce R, G and B images in parallel, and then the three images thus produced are composed. Recently, as a light valve element capable of fast switching, such as a ferroelectric liquid crystal display element or a digital micro-mirror device, is increasingly coming into practical use, a time-sharing single-panel method is widely used. In the time-sharing single-panel method, R, G and B lights are caused to sequentially impinge on one light valve element, the light valve element is driven in synchronization with switching-over of the R, G and B lights thereby producing R, G and B images in a time-series manner, and the images thus produced are projected onto a screen, or the like. Here, color composition of the images is accomplished by a viewer due to an afterimage effect occurring at a sense of vision. In the time-sharing single-panel method, reduction in both dimension and weight of the apparatus, which is a feature of a single-panel method, can be achieved by employing a relatively simple optical system, and therefore the time-sharing single-panel method is favorable for realizing inexpensive fabrication of a projection-type image display apparatus. In such an image display apparatus, a color wheel is preferably used as a filter element of a time-share light dispersing device to sequentially disperse light emitted from a white light source into R, G and B lights having respective wavelength bands in a time-sharing manner.
FIGS. 5A and 5B are respectively top plan and side views of a conventional and typical color wheel assembly 200 as a time-share light dispersing device including such a color wheel. Referring to FIG. 5B, the color wheel assembly 200 comprises a color wheel 150, and a driving motor 106 including a motor hub 105. The color wheel 150 is a tricolor color wheel and is composed of a disk-like substrate 101 made of a light-transmitting material, for example, optical glass, and three pie-shaped (sectorial) filters 102, 103 and 104 adapted to transmit exclusively, for example, R, G and B lights, respectively are formed on a surface of the substrate 10. The color wheel 150 thus structured is fixedly attached to the motor hub 105 coaxially therewith. The color wheel assembly 200 operates such that the color wheel 150 is spun by the driving motor 106 so that white light S impinges sequentially on the filters (R, G and B) 102, 103 and 104 whereby the white light S is sequentially dispersed into R. G and B lights.
There are two types of color wheel structures: a monolithic type structured such that respective color filters are formed on a disk-like substrate, such as the color wheel 150 described above; and a segment type structured such that respective color filter segments separately prepared in a sectorial shape are fixedly attached to one another so as to form a disk.
FIGS. 6 and 7 show respectively top plan and exploded side sectional view of a segment-type color wheel 160 comprising a plurality (four in FIG. 6) of sectorial color filter segments (hereinafter referred to simply as segments as appropriate) 112, 114, 116 and 118 which are separately prepared and are fixed in position by means of a support member 120 and a clamp member 122 so as to form a disk.
Specifically, as shown in FIG. 7, respective inner circumferences 112a, 114a, 116a and 118a of the segments 112, 114, 116 and 118 are fitted to an outer circumference of a smaller cylinder portion 120a of the support member 120 whereby the segments 112, 114, 116 and 118 are duly set in position in the radial direction of the color wheel 160, and respective surfaces of the segments 112, 114, 116 and 118 toward the inner circumferences 112a, 114a, 116a and 118a are fitted to an annular seat portion 120b of the support member 120 whereby the segments 112, 114, 116 and 118 are duly set in position in the thickness direction of the color wheel 160. Then, a smaller cylinder portion 122a of the clamp member 122 is engagingly inserted into a hollow 120c of the support member 120 so that an annular seat portion 122b of the clamp member 122 and the aforementioned annular seat portion 120b of the support member 120 sandwich and clamp the inner circumferential portions of the 112, 114, 116 and 118. And, when the support member 120 and the clamp member 122 are bonded or screwed together, the segments 112, 114, 116 and 118 are fixed in position. The color wheel 160 thus structured is fixedly attached to a hub (such as the hub 105 shown in FIGS. 5A and 5B) of a motor (such as the driving motor 106 shown FIG. 5B) such that the hub is inserted in a hollow 122c of the clamp member 122 (refer to, for example, Japanese Patent Applications Laid-Open Nos. 2004-101827 ([0010], and FIG. 6 therein) and H10-48542 (Claim 1, and FIG. 2 therein).
A monolithic-type color wheel structured with a single substrate makes it easy to maintain the geometric accuracy and therefore easy to hold down the generation of vibrations and noises at the time of spinning, but requires sophisticated processes of forming color filters on the substrate thus resulting in cost disadvantage. A segment-type color wheel has an advantage over the monolithic type in this respect, but requires a high degree of accuracy in positioning separately prepared segments and therefore must ultimately go through an alignment process for preventing the generation of vibrations and noises at the time of high speed spinning thus increasing the number of manufacturing processes. Also, in the segment-type color wheel, a support member is additionally required in order to accurately position color filter segments separately prepared, which not only results in an increased number of components, but also requires a very high dimensional precision on both the segments and the support member because the both components are prepared independently at different processes using respective equipments totally different from each other, and fitted together at a later step.